Various neurodegenerative disorders are characterized by selective degeneration of nigral dopaminergic neurons in the brain, including Parkinson's disease (PD). PD is the second most common neurodegenerative disorder after Alzheimer disease and affects more than 1.5 million people in the U.S. with approximately 50,000 to 60,000 new cases diagnosed each year. The disease is characterized by the cardinal motor symptoms of rigidity, bradykinesia, tremors and postural instability. Existing treatment options for neurodegenerative disorders fail to prevent the progression of the degeneration. As a result, development of neuroprotective agents to delay progression of the disease is needed. The apoptotic cell death pathway mediated by protein kinase C is a viable treatment pathway.
Protein kinase C (PKC) belongs to a family of serine threonine protein kinases. To date, twelve isoforms in the PKC subfamily have been identified (Kanthasamy et al., Antioxidants & Redox Signaling, 5: 609-620, 2003). One such isoform is protein kinase C delta (PKCδ) (Martelli et al., Eur. J. Histochem., 48(1):89-94, 2004).
PKCδ was originally discovered by Gschwendt et al. (Biochem. Biophys. Res. Commun., 137: 766-74, 1986) and cloned from a rat brain cDNA library the following year (Kurkinen et al., Gene 242: 115-23, 2000; Ono et al., Identification of three additional members of rat protein kinase C family: delta-, epsilon- and zeta-subspecies. FEBS Lett., 226: 125-8, 1987). The PKCδ gene is localized on human chromosome 3 (Huppi et al., Assignment of the protein kinase C delta polypeptide gene (PKCδ) to human chromosome 3 and mouse chromosome 14. Genomics 19: 161-2, 1994), rat chromosome 16 (Kurkinen et al., Genomic structure and chromosomal localization of the rat protein kinase C delta gene. Gene 242: 115-23, 2000), and mouse chromosome 14 (Huppi et al., Assignment of the protein kinase C delta polypeptide gene (PKCδ) to human chromosome 3 and mouse chromosome 14. Genomics. 19: 161-62, 1994).
Rottlerin exhibits biological activity, including selectively inhibiting protein kinase C delta (PKCδ). Rottlerin is a natural product that is isolated from the seeds of the fruit Mallotus philippinensis, most commonly produced in India, Philippines, Southeast Asia, and Australia. The IUPAC name for rottlerin is (E)-1-[6-[(3-acetyl-2,4,6-trihydroxy-5-methylphenyl)methyl]-5,7-dihydroxy-2,2-dimethylchromen-8-yl]-3-phenylprop-2-en-1-one. The molecular formula for the structure is C30H28O8 and the structure has a molecular weight of 516.53852 g/mol. The chemical structure of rottlerin is shown below:

Rottlerin selectively inhibits PKCδ with an IC50 of 3-6 μM. Although rottlerin is widely used as a specific inhibitor of PKCδ (McCormack et al., Neurobiol. Dis., 10(2): 119-27, 2002; Kanthasamy et al., Brain Res., 759(1): 1-8, 1997; Przedborski et al., Proc. Natl. Acad. Sci., 93(10): 4565-71, 1996), rottlerin has also been shown to inhibit PRAK, MAP kinases, and CAMKII kinases at higher concentrations (Turmel et al., Mov. Disord., 16(2): 185-9, 2001; Jackson-Lewis et al., Neurodegeneration, 4(3): 257-69, 1995).
Synthesis of rottlerin has not been reported. No studies of the scope and limitations of the preparation of rottlerin and/or any synthetic analogs have been reported. Similarly, there is a lack of detailed studies of the molecular mechanism of action of rottlerin; it is unknown what segments of the rottlerin structure are biologically active. However, documented uses of the rottlerin structure are known (see e.g., Kanthasamy et al. U.S. patent application Ser. Nos. 11/479,173 and 61/240,906) but are significantly restricted due to the limited natural abundance of the substance. Due to such limited abundance, rottlerin is cost prohibitive for use as a drug therapy, despite its identified beneficial actions as a PKCδ inhibitor. Accordingly, methods of rottlerin synthesis in large quantities are desirable in order to obtain sufficient quantities of the analog for future studies. Further, synthetic rottlerin that are PKCδ inhibitors with better selectivity and more affinity are desirable and an objective of the present invention.
Accordingly, it is an objective of the present invention to develop methods and means of synthesizing PKCδ inhibitor analogs from the rottlerin base structure.
It is a further objective of the present invention to develop rottlerin analogs having simplified chemical structures in order to identify analogs with enhanced biological activity compared to natural rottlerin.
It is a further objective of the present invention to develop methods of rottlerin analog synthesis from commercially-available materials comprising minimal synthesis steps, namely four or fewer synthesis steps.
The method and means of accomplishing each of the above objectives as well as others will become apparent from the detailed description of the invention which follows hereafter.